Immunohistochemical Detection of P-glycoprotein in Breast Cancer and Its Significance as a Prognostic Factor

Expression of multidrug resistance protein P-glycoprotein in correlation with markers of hypoxia (HIF-1α, EPO, EPO-R) in invasive breast cancer with metastasis to lymph nodes

INTRODUCTION

Overexpression of the mdr-1 gene is the earliest discovered mechanism of multidrug resistance, which is associated with P-glycoprotein (P-gp) - a cell membrane protein responsible for the efflux of drugs of various structures out of cancer cells. Although the expression of P-glycoprotein has been demonstrated in many cancer types, its relation to markers of hypoxia such as HIF-1α, EPO-R or EPO in invasive breast cancer is not well established. The aim of this research was to analyze the co-expression of P-glycoprotein and the markers of tissue hypoxia HIF-1α, EPO, and EPO-R by immunohistochemistry in invasive breast cancer classified according to the presence of steroid receptors and the HER2 receptors.

MATERIAL AND METHODS

Tissue samples were collected from 58 patients with the diagnosis of invasive breast cancer with lymph node metastases. The expression of P-gp, HIF-1α, EPO-R and EPO was determined by immunohistochemistry.

RESULTS

Of all the invasive breast cancers with lymph node metastases, 15.5% expressed P-gp in cell membrane and tumor blood vessels. In our research, there was a significant positive correlation between HER2-positive tumors that did not express steroid receptors (ER-/PR-/HER2+), and P-gp expression (p = 0.049, r = 0.105). Moreover, there was a significant positive correlation between EPO expression and P-gp (p < 0.001, r = 0.474), and between HIF-1α expression and P-gp (p = 0.00475, r = 0.371).

CONCLUSIONS

We found that HIF-1α and EPO expression is significantly associated with P-gp expression in invasive breast cancer with lymph node metastases. An important result of our study is the demonstration of a correlation between P-gp expression and patients with HER2-positive breast tumors that do not express steroid receptors.

Sensitivity of docetaxel-resistant MCF-7 breast cancer cells to microtubule-destabilizing agents including vinca alkaloids and colchicine-site binding agents

Introduction

One of the main reasons for disease recurrence in the curative breast cancer treatment setting is the development of drug resistance. Microtubule targeted agents (MTAs) are among the most commonly used drugs for the treatment of breaset cancer and therefore overcoming taxane resistance is of primary clinical importance. Our group has previously demonstrated that the microtubule dynamics of docetaxel-resistant MCF-7_TXT cells are insensitivity to docetaxel due to the distinct expression profiles of β-tubulin isotypes in addition to the high expression of p-glycoprotein (ABCB1). In the present investigation we examined whether taxane-resistant breast cancer cells are more sensitive to microtubule destabilizing agents including vinca alkaloids and colchicine-site binding agents (CSBAs) than the non-resistant cells.

Methods

Two isogenic MCF-7 breast cancer cell lines were selected for resistance to docetaxel (MCF-7_TXT) and the wild type parental cell line (MCF-7_CC) to examine if taxane-resistant breast cancer cells are sensitive to microtubule-destabilizing agents including vinca alkaloids and CSBAs. Cytotoxicity assays, immunoblotting, indirect immunofluorescence and live imaging were used to study drug resistance, apoptosis, mitotic arrest, microtubule formation, and microtubule dynamics.

Results

MCF-7_TXT cells were demonstrated to be cross resistant to vinca alkaloids, but were more sensitive to treatment with colchicine compared to parental non-resistant MCF-7_CC cells. Cytotoxicity assays indicated that the IC₅₀ of MCF-7_TXT cell to vinorelbine and vinblastine was more than 6 and 3 times higher, respectively, than that of MCF-7_CC cells. By contrast, the IC₅₀ of MCF-7_TXT cell for colchincine was 4 times lower than that of MCF-7_CC cells. Indirect immunofluorescence showed that all MTAs induced the disorganization of microtubules and the chromatin morphology and interestingly each with a unique pattern. In terms of microtubule and chromain morphology, MCF-7_TXT cells were more resistant to vinorelbine and vinblastine, but more sensitive to colchicine compared to MCF-7_CC cells. PARP cleavage assay further demonstrated that all of the MTAs induced apoptosis of the MCF-7 cells. However, again, MCF-7_TXT cells were more resistant to vinorelbine and vinblastine, and more sensitive to colchicine compared to MCF-7_CC cells. Live imaging demonstrated that the microtubule dynamics of MCF-7_TXT cells were less sensitive to vinca alkaloids, and more sensitive to colchicine. MCF-7_TXT cells were also noted to be more sensitive to other CSBAs including 2MeOE₂, ABT-751 and phosphorylated combretastatin A-4 (CA-4P).

Conclusion

Docetaxel-resistant MCF-7_TXT cells have demonstrated cross-resistance to vinca alkaloids, but appear to be more sensitive to CSBAs (colchicine, 2MeOE₂, ABT-751 and CA-4P) compared to non-resistant MCF-7_CC cells. Taken together these results suggest that CSBAs should be evaluated further in the treatment of taxane resistant breast cancer.

Targeted Proteomics Enables Simultaneous Quantification of Folate Receptor Isoforms and Potential Isoform-based Diagnosis in Breast Cancer

The distinct roles of protein isoforms in cancer are becoming increasingly evident. FRα and FRβ, two major isoforms of the folate receptor family, generally have different cellular distribution and tissue specificity. However, the presence of FRβ in breast tumors, where FRα is normally expressed, complicates this situation. Prior to applying any FR isoform-based diagnosis and therapeutics, it is essential to monitor the expression profile of FR isoforms in a more accurate manner. An LC-MS/MS-based targeted proteomics assay was developed and validated in this study because of the lack of suitable methodology for the simultaneous and specific measurement of highly homologous isoforms occurring at low concentrations. FRα and FRβ monitoring was achieved by measuring their surrogate isoform-specific peptides. Five human breast cell lines, isolated macrophages and 60 matched pairs of breast tissue samples were subjected to the analysis. The results indicated that FRβ was overexpressed in tumor-associated macrophages (TAMs) but not epithelial cells, in addition to an enhanced level of FRα in breast cancer cells and tissue samples. Moreover, the levels of the FR isoforms were evaluated according to the histology, histopathological features and molecular subtypes of breast cancer. Several positive associations with PR/ER and HER2 status and metastasis were revealed.

Mechanisms of endocrine resistance in breast cancer: an overview of the proposed roles of noncoding RNA

Endocrine therapies such as tamoxifen and aromatase inhibitors are the standard treatment options for estrogen receptor-positive breast cancer patients. However, resistance to these agents has become a major clinical obstacle. Potential mechanisms of resistance to endocrine therapies have been identified, often involving enhanced growth factor signaling and changes in the expression or action of the estrogen receptor, but few studies have addressed the role of noncoding RNA (ncRNA). Two important types of ncRNA include microRNA (miRNA) and long noncoding RNA (lncRNA). miRNAs are small RNA molecules that regulate gene expression via translational inhibition or degradation of mRNA transcripts, while lncRNAs are larger RNA molecules that have been shown to play a role in multiple cellular maintenance functions such as protein scaffolding, chromatin looping, and regulation of mRNA stability. Both miRNA and lncRNA have recently impacted the field of breast cancer research as important pieces in the mechanistic puzzle of the genes and pathways involved in breast cancer development and progression. This review serves as an overview of the roles of miRNA and lncRNA in breast cancer progression and the development of endocrine resistance. Ideally, future experiments in the field should include identification of ncRNAs that could be potential therapeutic targets in endocrine-resistant tumors, as well as ncRNA biomarkers that facilitate more tumor-specific treatment options for endocrine-resistant breast cancer patients.

Evaluating the response of neoadjuvant chemotherapy for treatment of breast cancer: are tumor biomarkers and dynamic contrast enhanced MR images useful predictive tools?

OBJECTIVE

In order to evaluate the therapeutic response to neoadjuvant chemotherapy (NAC) for breast cancer, this research focused on the changes in expression of tumor biomarkers and the correlations associated with changes of magnetic resonance imaging (MRI) pre- and post-NAC. We also compared the accuracy of MRI and pathology in terms of residual tumor extent after NAC.

METHODS

MRI was performed before and after four courses of cyclophosphamide, epirubicin and paclitaxel (CET) NAC on 114 patients treated in Huashan Hospital (Fudan University) from December 2009 to January 2013. All patients were pathologically diagnosed with invasive breast cancer via core needle biopsy. A series of tumor biomarkers, including P-glycoprotein (P-gp) and Ki-67, was tested by immunohistochemistry in both core needle biopsy and surgical specimens. The changes in tumor biomarker expression and the shrinkage of tumor on MRI were observed. The residual tumor extent after NAC was compared in terms of MRI and histopathology, and the accuracy of MRI was evaluated by both residual tumor extent and by NAC therapeutic effect. Together, these methods enabled a prognostic estimate of NAC.

RESULTS

The P-gp expression before NAC was used to evaluate the therapeutic effect of NAC. The up-regulation of P-gp expression after NAC was associated with poor therapeutic effect (P=0.0011). The expression of Ki-67 was significantly down-regulated (P<0.0001) but it had no association with NAC response (P=0.9645). The mean extent of residual tumor after NAC as seen on MRI was 20.83 mm (±4.14 mm, 95% CI) and that of surgically removed specimens, 18.89 mm (±3.71 mm, 95% CI). The sensitivity of MRI was 95.1%, the specificity was 28.6%, the positive predictive value was 79.6%, and the negative predictive value was 66.7%.

CONCLUSIONS

P-gp status was an important factor affecting the pathological complete response (pCR) rate. The change in P-gp expression, from negative to positive following NAC treatment, indicated the emergence of drug resistance resulting from chemotherapy. The down-regulation of Ki-67 was associated with the decline of tumor proliferation. However, compared to the pre-NAC P-gp status, the pre-NAC Ki-67 status had little prognostic value. Additionally, the evaluation of the efficacy of NAC by either MRI or histopathology was inconclusive.

Multiple mechanisms underlying acquired resistance to taxanes in selected docetaxel-resistant MCF-7 breast cancer cells

Background

Chemoresistance is a major factor involved in a poor response and reduced overall survival in patients with advanced breast cancer. Although extensive studies have been carried out to understand the mechanisms of chemoresistance, many questions remain unanswered.

Methods

In this research, we used two isogenic MCF-7 breast cancer cell lines selected for resistance to doxorubicin (MCF-7_DOX) or docetaxel (MCF-7_TXT) and the wild type parental cell line (MCF-7_CC) to study mechanisms underlying acquired resistance to taxanes in MCF-7_TXT cells. Cytotoxicity assay, immunoblotting, indirect immunofluorescence and live imaging were used to study the drug resistance, the expression levels of drug transporters and various tubulin isoforms, apoptosis, microtubule formation, and microtubule dynamics.

Results

MCF-7_TXT cells were cross resistant to paclitaxel, but not to doxorubicin. MCF-7_DOX cells were not cross-resistant to taxanes. We also showed that multiple mechanisms are involved in the resistance to taxanes in MCF-7_TXT cells. Firstly, MCF-7_TXT cells express higher level of ABCB1. Secondly, the microtubule dynamics of MCF-7_TXT cells are weak and insensitive to the docetaxel treatment, which may partially explain why docetaxel is less effective in inducing M-phase arrest and apoptosis in MCF-7_TXT cells in comparison with MCF-7_CC cells. Moreover, MCF-7_TXT cells express relatively higher levels of β2- and β4-tubulin and relatively lower levels of β3-tubulin than both MCF-7_CC and MCF-7_DOX cells. The subcellular localization of various β-tubulin isoforms in MCF-7_TXT cells is also different from that in MCF-7_CC and MCF-7_DOX cells.

Conclusion

Multiple mechanisms are involved in the resistance to taxanes in MCF-7_TXT cells. The high expression level of ABCB1, the specific composition and localization of β-tubulin isoforms, the weak microtubule dynamics and its insensitivity to docetaxel may all contribute to the acquired resistance of MCF-7_TXT cells to taxanes.

Neoadjuvant chemotherapy induces expression levels of breast cancer resistance protein that predict disease-free survival in breast cancer

Three main xenobiotic efflux pumps have been implicated in modulating breast cancer chemotherapy responses. These are P-glycoprotein (Pgp), Multidrug Resistance-associated Protein 1 (MRP1), and Breast Cancer Resistance Protein (BCRP). We investigated expression of these proteins in breast cancers before and after neoadjuvant chemotherapy (NAC) to determine whether their levels define response to NAC or subsequent survival. Formalin-fixed paraffin-embedded tissues were collected representing matched pairs of core biopsy (pre-NAC) and surgical specimen (post-NAC) from 45 patients with invasive ductal carcinomas. NAC regimes were anthracyclines +/− taxanes. Immunohistochemistry was performed for Pgp, MRP1 and BCRP and expression was quantified objectively using computer-aided scoring. Pgp and MRP1 were significantly up-regulated after exposure to NAC (Wilcoxon signed-rank p = 0.0024 and p<0.0001), while BCRP showed more variation in response to NAC, with frequent up- (59% of cases) and down-regulation (41%) contributing to a lack of significant difference overall. Pre-NAC expression of all markers, and post-NAC expression of Pgp and MRP1 did not correlate with NAC response or with disease-free survival (DFS). Post-NAC expression of BCRP did not correlate with NAC response, but correlated significantly with DFS (Log rank p = 0.007), with longer DFS in patients with low post-NAC BCRP expression. In multivariate Cox regression analyses, post-NAC BCRP expression levels proved to predict DFS independently of standard prognostic factors, with high expression associated with a hazard ratio of 4.04 (95% confidence interval 1.3–12.2; p = 0.013). We conclude that NAC-induced expression levels of BCRP predict survival after NAC for breast cancer, while Pgp and MRP1 expression have little predictive value.

Reversing multidrug resistance in breast cancer cells by silencing ABC transporter genes with nanoparticle-facilitated delivery of target siRNAs

Background

Multidrug resistance, a major impediment to successful cancer chemotherapy, is the result of overexpression of ATP-binding cassette (ABC) transporters extruding internalized drugs. Silencing of ABC transporter gene expression with small interfering RNA (siRNA) could be an attractive approach to overcome multidrug resistance of cancer, although delivery of siRNA remains a major hurdle to fully exploit the potential of siRNA-based therapeutics. Recently, we have developed pH-sensitive carbonate apatite nanoparticles to efficiently carry and transport siRNA across the cell membrane, enabling knockdown of the cyclin B1 gene and consequential induction of apoptosis in synergy with anti-cancer drugs.

Methods and results

We report that carbonate apatite-mediated delivery of the siRNAs targeting ABCG2 and ABCB1 gene transcripts in human breast cancer cells which constitutively express both of the transporter genes dose-dependently enhanced chemosensitivity to doxorubicin, paclitaxel and cisplatin, the traditionally used chemotherapeutic agents. Moreover, codelivery of two specific siRNAs targeting ABCB1 and ABCG2 transcripts resulted in a more robust increase of chemosensitivity in the cancer cells, indicating the reversal of ABC transporter-mediated multidrug resistance.

Conclusion

The delivery concept of multiple siRNAs against ABC transporter genes is highly promising for preclinical and clinical investigation in reversing the multidrug resistance phenotype of breast cancer.

The risk of recurrence in breast cancer patients treated with tamoxifen: polymorphisms of CYP2D6 and ABCB1

CYP2D6 plays a major role in the metabolism of tamoxifen, and polymorphism of P-glycoprotein has been associated with resistance of many drug therapies. This study investigates the clinical impact of genetic variants of CYP2D6 and ABCB1 in breast cancer patients treated with tamoxifen. Blood samples from 95 breast cancer patients treated with tamoxifen were collected and genotyped for CYP2D6 and ABCB1 variants using allele-specific PCR method. Recurrence risks were calculated using Kaplan-Meier analysis and compared using the log-rank test. Patients carrying CYP2D6*10/*10 and heterozygous null allele (IM) showed higher risks of developing recurrence and metastasis (OR 13.14; 95% CI 1.57-109.94; P = 0.004) than patients with CYP2D6*1/*1 and *1/*10 genotypes. Patients with homozygous CC genotypes of ABCB1 C3435T showed a shorter time to recurrence. Patients who were CYP2D6 IM and homozygous CC genotype of C3435T have statistically significant higher risks of recurrence (P = 0.002). Similarly, median time to recurrence in these patients was only 12 months (95% CI = 0.79-23.2) compared to those without this combination which was 48 months (95% CI = 14.7-81.2). Patients with CYP2D6 IM and homozygous CC genotype of ABCB1 C3435T have shorter times to recurrence. The results confirmed the findings of previous studies and support FDA recommendation to perform pre-genotyping in patients before the choice of therapy is determined in breast cancer patients.

Chemotherapy resistance in metastatic breast cancer: the evolving role of ixabepilone

Resistance to chemotherapy is a major obstacle to the effective treatment of many tumor types. Although many anticancer therapies can alter tumor growth, in most cases the effect is not long lasting. Consequently, there is a significant need for new agents with low susceptibility to common drug resistance mechanisms in order to improve response rates and potentially extend survival. Approximately 30% of the women diagnosed with early-stage disease in turn progress to metastatic breast cancer, for which therapeutic options are limited. Current recommendations for first-line chemotherapy include anthracycline-based regimens and taxanes (paclitaxel and docetaxel). They typically give response rates of 30 to 70% but the responses are often not durable, with a time to progression of 6 to 10 months. Patients with progression or resistance may be administered capecitabine, gemcitabine, vinorelbine, albumin-bound paclitaxel, or ixabepilone, while other drugs are being evaluated. Response rates in this setting tend to be low (20 to 30%); the median duration of responses is <6 months and the results do not always translate into improved long-term outcomes. The present article reviews treatment options in taxane-resistant metastatic breast cancer and the role of ixabepilone in this setting.

Implications of anthracycline-resistant and taxane-resistant metastatic breast cancer and new therapeutic options

Patients with advanced or metastatic breast cancer commonly develop disease resistant to chemotherapy (typically anthracyclines and taxanes), which presents a major obstacle to therapy and leaves few effective treatment options. Drug resistance can occur due to various mechanisms including modification of drug efflux membrane transporters such as P-glycoprotein, as well as alterations in beta-tubulin. The novel epothilone B analog, ixabepilone, which has low susceptibility to various drug-resistance mechanisms, has demonstrated preclinical activity in drug-resistant breast cancer. The clinical activity of ixabepilone was evaluated in metastatic breast cancer patients with highly pretreated and/or resistant/refractory disease. Results were reviewed from three phase II trials in which ixabepilone was administered as monotherapy and one phase III trial that evaluated ixabepilone in combination with capecitabine. As a single agent, ixabepilone demonstrated activity in women who were heavily pretreated and resistant to an anthracycline, a taxane, and/or capecitabine. The combination of ixabepilone and capecitabine was significantly more active than capecitabine alone in patients with prior treatment or resistance to anthracyclines and taxanes. Treatment-related adverse events were generally low grade except for grade 3/4 toxicities, including neutropenia (53-54%) and reversible peripheral sensory neuropathy (14-16%). Ixabepilone has significant activity in patients with heavily pretreated metastatic breast cancer who are disease resistant or refractory to anthracyclines and taxanes. Further clinical evaluation of this agent in patients with drug-resistant breast cancer and in specific patient subsets is warranted.

Improvement of tumor targeting and antitumor activity by a disulphide bond stabilized diabody expressed in Escherichia coli

We have generated an anti-Pgp/anti-CD3 diabody which can effectively inhibit the growth of multidrug-resistant human tumors. However, the two chains of the diabody are associated non-covalently and are therefore capable of dissociation. Cysteine residues were introduced into the V-domains to promote disulphide cross-linking of the dimer as secreted by Escherichia coli. Compared with the parent diabody, the ds-Diabody obtained was more stable in human serum at 37 degrees C, without loss of affinity or cytotoxicity activity in vitro. Furthermore, the ds-Diabody showed improved tumor localization and a twofold improved antitumor activity over the parent diabody in nude mice bearing Pgp-overexpressing K562/A02 xenografts. Our data demonstrate that ds-Diabody may be more useful in therapeutic applications than the parent diabody.

Role of ABCB1 and ABCC1 gene induction on survival in locally advanced breast cancer

Drug resistance to chemotherapy in patients with locally advanced breast cancer results in a decrease in treatment efficacy and in patient survival. This study aimed to evaluate the impact of ABCB1 and ABCC1 gene induction during chemotherapy on disease-free and overall survival of breast cancer patients. Patients with locally advanced breast cancer were prospectively included. All patients were preoperatively treated with chemotherapy and underwent mastectomy. ABCB1 and ABCC1 gene and protein expressions were evaluated both before and after chemotherapy and investigated as molecular predictive parameters affecting diseasefree and overall survival. ABCB1 and ABCC1 gene expressions were evaluated with RTPCR following RNA isolation from tissue samples. P-glycoprotein and MRP1 in tissues were detected using immunohistochemistry. Twenty-five female patients treated with either doxorubicin or epirubicin were included. Median follow-up time was 36 months during which 11 patients (44%) had recurrence, all of whom died. Mean disease-free survival for patients with and without ABCB1 gene induction was 13 and 55 months (p=0.0004), respectively, whereas overall survival was 21 and 57 months (p=0.0025), respectively. Mean disease-free survival for patients with and without ABCC1 gene induction was 32 and 48 months (p=0.97), respectively, and overall survival was 43 and 49 months (p=0.36), respectively. ABCB1 gene induction decreases disease-free and overall survival in patients with locally advanced breast cancer due to anthracycline resistance. Detecting ABCB1 gene expression during chemotherapy helps to increase the efficacy of drug treatment by choosing the appropriate drugs resulting in prolonged survival.

Association of the ABCB1 gene polymorphisms 2677G>T/A and 3435C>T with clinical outcomes of paclitaxel monotherapy in metastatic breast cancer patients

BACKGROUND

ABCB1 is responsible for multidrug resistance, the principal mechanism by which many cancers develop resistance to chemotherapeutic drugs. There is a controversy whether ABCB1 gene polymorphisms correlate with survival and response in cancer patients treated with chemotherapy. We evaluated the association between clinical outcome (safety and efficacy) of paclitaxel monotherapy in metastatic breast cancer patients with ABCB1 gene polymorphisms 2677G>T/A or 3435C>T.

PATIENTS AND METHODS

Patients with metastatic breast cancer were treated with 175 mg/m(2) paclitaxel per 3-week cycle. Peripheral blood mononuclear cells from patients were used to genotype ABCB1 2677G>T/A and 3435C>T polymorphisms. Genotypes were investigated for their association with tumor response, survival, toxicity, and chemoresistance.

RESULTS

ABCB1 3435 CT showed a significantly lower disease control rate than the CC genotype (P = 0.025). ABCB1 3435 CT was correlated with shorter overall survival (OS) in Cox regression analysis (P = 0.026). The 2677 GG genotype showed a significant association with chemoresistance to paclitaxel and anthracycline (P = 0.04 and 0.04, respectively). None of the ABCB1 genotypes correlated with toxicity.

CONCLUSIONS

ABCB1 genotypes may be a predictor of paclitaxel activity as well as a prognostic factor in metastatic breast cancer patients.

Expression of the multidrug resistance proteins MRP2 and MRP3 in human cholangiocellular carcinomas

BACKGROUND

Cholangiocellular carcinomas and gallbladder carcinomas are highly aggressive tumours with a poor prognosis and are generally regarded as chemoresistant tumours. Overexpression of ATP-binding cassette transporters of the multidrug resistance protein (MDR) and multidrug resistance-related protein (MRP) family in cancer cells is a major cause for the multidrug resistance phenotype in vitro and in vivo. To further define the role of MRP family members in biliary tract cancer, we studied the expression and localization of MRP2 and MRP3 in cholangiocellular carcinomas and gallbladder carcinomas.

MATERIALS AND METHODS

The expression and cellular localization of the multidrug resistance proteins MRP2 and MRP3 in human cholangiocellular carcinomas and gallbladder carcinomas were analysed by immunohistochemistry using isoform-specific antibodies. Expression of MRP isoforms was studied in vitro in Mz-ChA-1 cells derived from gallbladder adenocarcinoma by reverse transcription-polymerase chain reaction (RT-PCR), immunoblotting and immunofluorescence microscopy.

RESULTS

Mz-ChA-1 cells constitutively expressed MDR P-glycoproteins, MRP1, MRP2 and MRP3 by RT-PCR, immunoblotting and immunofluorescence microscopy. MRP2 and MRP3 are expressed in the respective apical and basolateral membrane domains. MRP3 was the predominant MRP isoform in gallbladder carcinomas (93%) and cholangiocellular carcinomas (57%), whereas MRP2 expression was detected in only 29% of gallbladder carcinomas and was undetectable in cholangiocellular carcinomas.

CONCLUSIONS

Our findings suggest that the intrinsic multidrug resistance of cholangiocellular and gallbladder carcinomas seems to be independent of MRP2 expression while the expression of MRP3 may contribute to the MDR phenotype.

Taxanes, microtubules and chemoresistant breast cancer

The taxanes, paclitaxel and docetaxel are microtubule-stabilizing agents that function primarily by interfering with spindle microtubule dynamics causing cell cycle arrest and apoptosis. However, the mechanisms underlying their action have yet to be fully elucidated. These agents have become widely recognized as active chemotherapeutic agents in the treatment of metastatic breast cancer and early-stage breast cancer with benefits gained in terms of overall survival (OS) and disease-free survival (DFS). However, even with response to taxane treatment the time to progression (TTP) is relatively short, prolonging life for a matter of months, with studies showing that patients treated with taxanes eventually relapse. This review focuses on chemoresistance to taxane treatment particularly in relation to the spindle assembly checkpoint (SAC) and dysfunctional regulation of apoptotic signaling. Since spindle microtubules are the primary drug targets for taxanes, important SAC proteins such as MAD2, BUBR1, Synuclein-gamma and Aurora A have emerged as potentially important predictive markers of taxane resistance, as have specific checkpoint proteins such as BRCA1. Moreover, overexpression of the drug efflux pump MDR-1/P-gp, altered expression of microtubule-associated proteins (MAPs) including tau, stathmin and MAP4 may help to identify those patients who are most at risk of recurrence and those patients most likely to benefit from taxane treatment.

Molecular markers of multiple drug resistance in breast cancer

Breast cancer is a significant health problem in terms of both morbidity and mortality, with approximately 12% of women directly affected by this disease. Chemotherapy, given to patients with earlier stage disease, has a good survival impact and may contribute to cure. The failure of chemotherapeutic drugs to eradicate cancer cells in more advanced disease states may be due to intrinsic or acquired drug resistance, including multiple drug resistance. The drug resistance observed in breast cancer patients is likely to be multifactorial, involving mechanisms such as altered expression and/or activity of drug efflux pumps, nuclear DNA-binding enzymes, metabolizing and conjugating enzymes, and mismatch repair deficiency. More extensive transcriptomic and proteomic analyses of breast tumour and normal biopsies, followed by functional genomic studies in relevant cell line models, should increase our understanding of this phenomenon and lead to therapies being individualized for identifiable subgroups of breast cancer patients.

Tesmilifene may enhance breast cancer chemotherapy by killing a clone of aggressive, multi-drug resistant cells through its action on the p-glycoprotein pump

Tesmilifene is a novel potentiator of chemotherapy which, when added to doxorubicin, achieved an unexpected and very large survival advantage over doxorubicin alone in a randomized trial in advanced breast cancer. This trial was unusual in that the early endpoints (response rate and median progression-free survival) were equivalent in the two arms, despite the ultimate survival difference. These aspects, coupled with the absence of a coherent molecular mechanism of action, and a pending confirmatory trial, have led oncologists to hold judgement on this drug. This paper reacts to this in three ways: firstly, a forensic subgroup analysis is presented with an explanation as to why it strongly supports the veracity of the survival difference; secondly a novel cellular explanation is provided for the decoupling of the early and late (survival) endpoints; finally, a molecular mechanism of action is proposed, for the first time, which reconciles the peculiarities of the trial with the laboratory data and background literature. This hypothesis explains how tesmilifene could meld two of the apparent strengths of the cancer cell (drug resistance pumps, and hypoxia-adapted energetics) into a potent weapon of self-destruction. Tesmilifene is proposed to allow chemotherapy (e.g. anthracycline or taxane) to additionally kill a small but critical population (clone) of aggressive, multi-drug resistant cells, the benefits of which cannot be appreciated until a period of time (about 6-8 months) has elapsed. These cells, present in women with more rapidly relapsing disease, very likely carry an energy-dependent extrusion pump which is paradoxically activated by tesmilifene plus the chemotherapy. The result is that, despite the chemotherapy's remaining extracellular, the cell dies from reactive oxygen species leaking from the electron chain transport in the abnormal mitochondria which characterize cancer. These mitochondria are activated in response to the ATP cost of this pump activation, in these predominantly glycolytic cells.

Increased expression of MDR1 mRNAs and P-glycoprotein in placentas from HIV-1 infected women

P-glycoprotein transports several compounds including protease inhibitors, actually used in the clinical management of HIV-1 infection. Since P-glycoprotein is expressed in placental trophoblasts, its efflux activity could interfere with placental transfer of antiretrovirals. The purpose of this study was to investigate the expression of P-gp-encoding MDR1 gene and P-gp itself in full-term placentas from uninfected (n=35) and HIV-1 infected women (n=24). MDR1 transcripts were quantified by real-time PCR using relative (MDR1 normalized upon 28S levels) and absolute (copy number) determinations. P-glycoprotein localization and expression were evaluated by immunohistochemistry and western blot analysis, respectively. Relative or absolute PCR quantification showed a significant 3.3-fold (p<0.0009) or 3.7-fold (p<0.0002) mean increase in MDR1 placental transcription in HIV-infected compared to non-infected women, respectively. Ratios of individual HIV-positive values to HIV-negative mean ranged from 0.1 to 21.8. Moreover a significant 2.5-fold increased expression of immunoreactive P-glycoprotein was evidenced in placentas from HIV-infected women (p<0.0001). This MDR1 overexpression was observed in a similar extent in placentas from pregnant women treated with Zidovudine alone or in combination with Nelfinavir and/or Lamivudine. Our findings suggest that P-glycoprotein in placentas from HIV-infected women would contribute to modulate the materno-fetal transport of antiretrovirals across the placental barrier and consequently diminish fetal exposure to these compounds.

Efficient inhibition of multidrug-resistant human tumors with a recombinant bispecific anti-P-glycoprotein × anti-CD3 diabody

Overexpressing of P-glycoprotein (Pgp) has been shown to be responsible for cancer resistance to multiple chemotherapeutic agents. Immunotherapy with biological agents, such as bispecific antibodies (BsAbs), may represent a promising approach to overcome the emergence of drug resistance. Here we constructed a recombinant BsAb, a diabody, with specificities to both CD3 on human T-lymphocyte and Pgp on cancer cells. The diabody was produced in Escherichia coli in a soluble functional form and purified by an affinity chromatography with a yield of >4 mg/l culture medium in shaker flask. The diabody binds to both CD3 on T-lymphocytes and Pgp on multidrug-resistant (MDR) tumor cells with affinities that are comparable to its respective parental single chain Fv molecules. In the presence of activated human peripheral blood lymphocytes (PBLs), the diabody mediates effectively the lysis of the Pgp-overexpressing human leukemia K562/A02 and epidermoid carcinoma KBv(200) cells, but is much less potent in mediating the lysis of the parent K562 and KB cells. Further, the diabody localized selectively within the K562/A02 xenografts in mice. When combined with activated PBL, the diabody significantly inhibited the growth of K562/A02 and KBv(200), but had no effect on K562 and KB xenografts. In contrast, treatment with doxorubicin, a standard chemotherapeutic agent, only inhibited the growth of K562 and KB, but had no effect on K562/A02 and KBv(200) xenografts. Taken together, our results suggest that the anti-Pgp x anti-CD3 diabody may have a great potential in the treatment of various MDR cancers.